1. Field of the Invention
This invention relates to an electrode for connecting an electric wire to a heated body which is heated to a high temperature. More specifically, this invention relates to an electrode structure of an electrically heated-type catalyst device.
2. Description of the Related Art
An electrically heated-type catalyst device which is heated by electricity to quickly activate a catalyst after the start from a cold state is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 6-108831. According to the device, one end of a solid stud bolt is connected to a catalyst while the other end is extended to the outside of an exhaust pipe and is connected to an external wire. Generally, a copper cable (copper wire) is used in most cases as the external electric wire.
However, because the junction between the stud bolt and the external electric wire exists in the proximity of the catalyst, the junction is likely to be heated by the catalyst through the stud bolt and attains a high temperature, or the junction on the stud bolt side is likely to undergo high temperature oxidation and invites conduction failure. Further, the external electric wire, too, attains a high temperature, so that problems such as the material change of the electric wire itself or deterioration of a covering material occur.
These problems may be solved, in principle, by extending the length of the lead-out electrode so as to bring the junction away from the catalyst. But according to this arrangement, the resistance value of the lead-out electrode itself becomes so great that the catalyst itself cannot be heated sufficiently or the weight of the lead-out electrode becomes great. In addition, such a large lead-out electrode is more likely to interfere with other components and its mountability is poor.
In view of the problems described above, the present invention aims at lowering the temperature at the junction between the lead-out electrode of the electrically heated-type catalyst device and the external electric wire without increasing the resistance value.
According to the present invention, there is provided a structure of an electrode for connecting an external electric wire to a heated body heated to a high temperature, which comprises a high temperature side electrode made of a conductor and connected to the heated body; and a low temperature side electrode connected at a first end thereof to the high temperature side electrode and having a second end portion thereof connected to the external electric wire; wherein the low temperature side electrode is produced by covering a material changes and conduction defects develop in the prior art devices. However, in the present invention, because the conductor of the low temperature side electrode is made of a material having a lower conduction resistivity than that of the conductor of the high temperature side electrode.
The present invention may be more fully understood from the description of preferred embodiments thereof set forth below, together with the accompanying drawings.